The present invention relates to an installation and a method for driving a scraper for subsea pipes.
One envisioned field of application is particularly that of rigid subsea pipes designed for transporting hydrocarbons which need to have scrapers or “pigs” driven along inside them in order to clean them or to inspect them using inspection devices.
Customarily, subsea pipes are laid on the seabed where there is a hydrostatic pressure that is determined by the depth of water above. They are equipped at each of their two opposite ends with devices that allow the scraper to be propelled along inside the pipe.
One of the ends is equipped with a launch device in which the scraper is initially installed, while the other end is equipped with a receiver trap device that allows the scraper to be retrieved once it has been launched by the launch device and driven in its sliding movement through the pipe.
In order to be able to propel this scraper through a pipe, the scraper needs to have translational mobility while at the same time demarcating the pipe into two appreciably watertight chambers, an upstream chamber at the launch device end and a downstream chamber at the receiver trap device end. With said pipe initially at an internal pressure lower than said hydrostatic pressure, for example at atmospheric pressure, the scraper is then launched into said pipe from said launch device toward said receiver trap device, allowing water from said seabed to enter via said launch device in order to bring said upstream chamber to said hydrostatic pressure.
Reference may be made to document WO 97/10943, which describes such a scraper and an installation that allows it to be moved along inside a pipe in order in particular to drive a riser therein.
However, the pipes between the launch device and the receiver trap device are sometimes damaged and deformed and are usually appreciably indented without necessarily being punctured, and this prevents the translational movement of the scraper. It then becomes necessary to dismantle the pipe or, sometimes, to section it in order to be able to retrieve the scraper. Such measures are quite obviously expensive.
One problem that arises and that the present invention aims to solve is therefore that of providing an installation and a method for driving a scraper that allows such measures to be avoided.